I have a Hauppauge WinTV-GO card that I use to watch TV and play video games on. It has the video (yellow plug) for things like video games. For audio, I bought a little plug from radioshack that converts the red and white audio plugs into a single 1/8th inch (headphone size plug) that you just plug into the audio-in on your sound card. This setup works great for watching TV/playing games on your screen because it comes with great software for it that lets you record video, take still snapshots up to 1600x1200, lets you label channels, and a ton of other great stuff. The screen is a window that can be resized to however big you like, letting you do other stuff on your computer at the same time. It also goes straight from the TV tuner card (PCI) to your video card, which means it doesn't hog up any system memory at all.
The only problem is quality. I recently found out that there is no way around the low quality that you get with a TV tuner in your PC. It's because the resolution of a TV is much smaller than that of a PC. It's not HORRIBLE quality, meaning you can get used to it, but it won't take advantage of a high res monitor. If you scale the size of the window down to about 640x480 or so, it looks great. Somebody here also told me not long ago that you can get a converter that lets you plug your monitor right into it (bypassing your computer completely), but the resolution issue remains.
I was pretty pissed when I plugged in my new TV card a couple weeks ago and found out how low the quality is. But i've gotten used to it, and usually run it at about 800x600 with little to complain about. If you're going to buy a TV tuner, I definitly recommend Hauppauge:
http://www.hauppauge.com/Pages/produ...ta_goplus.html It's only $50 too.